1. Field of the Invention
The present invention relates to a process for dyeing of cotton yarns, more specifically, to an improved rope dyeing process for fashion dyeing cotton yarns such as denim cotton yarns using an oxidizable indigo derivative, and to the dyed articles thus obtained.
2. Background of the Invention
Denim is a fabric widely used for working clothes, female dresses and children's clothes because of its good feeling and the toughness of the cotton yarn from which the denim is woven.
Of the clothes made of denim fabric, blue jeans are the most prevalent. Reasons why blue jeans are used in large quantities are the unique hue of clothes made from woven fabric dyed with an indigo dye and the change in that hue which occurs with time and washings or by bleaching which are favored so that it is possible to design articles of clothing based on this sensitiveness to hue change
In recent years, fashion dyed, i.e., jeans fabricated from denim fabric woven from yarn dyed a clear blue color are in demand as a result of variety and individuality of the fashion.
In order to meet the demand for brilliant blue jeans, many investigations have been made using indigo dyes, but a satisfactory brilliant blue color has not yet been achieved. Research has also been conducted using sulfur dyes, vat dyes, reactive dyes and naphthol dyes. However, the dyeing mechanism of these dyes is very different from indigo dyes and, for this reason, it is difficult to employ these dyes in conventional rope dyeing equipment adapted for use with an indigo dye. In addition, the decoloration effect of these dyes with chlorine bleaching is minimal at best, and therefore the commercial value of the blue jeans dyed with using these dyes is noticeably low.
Indigo derivatives are known which produce a clear hue similar to indigo However, when denim cotton yarns are dyed in rope form with these indigo derivatives in a conventional indigo dyeing process, a brilliant speciality colors and effects cannot be attained.